Exchange 2003: Mailbox Move across WAN

Would like to pick your brains on this one.  Running Exchange 2003.  Need to move a 1.5 GB mailbox across the WAN.  Did a test move by exmerging a copy of the relevant user's mailbox and attaching it to a test account.  Ran the move and it completed 20% over 8 hours.  It's a bit too long.  Had a few ideas and wanted to know which option you thought was best.  Any data loss is unacceptable.  

1)  Just run the traditional mailbox move over the weekend and wait it out.

2)  Exmerge the user's mailbox to PST.  Delete the contents of the mailbox to bring the size down to next to nothing.  Move the empty mailbox.  Import the PST into the mailbox after it's moved.  

3)  Right now we have the user setup to use Cached Exchange Mode.  We can therefore take a copy of the OST file and convert it to a PST.  We would reconfigure the Outlook profile to not use Cached Exchange, launch Outlook, delete the mailbox contents, move the empty mailbox, then Exmerge in the PST that we converted to OST.